Superconductivity and antiferromagnetic ordering in the high-field paramagnetic oxypnictide NdFeAsO0.94F0.06

We present measurements of the temperature and field dependencies of the magnetization M (T,H) of NdFeAsO(0.94)F(0.06) at fields up to 33 T to probe the coexistence of superconductivity with global antiferromagnetic ordering. Although M (T,H) at 48 < T < 140 K exhibits a clear Curie-Weiss temperature dependence corresponding to the Neel temperature T(N) approximate to 11-12 K, the behavior of M(T,H) below T(c) is only consistent with either paramagnetism of weakly interacting magnetic moments or perhaps a spin-glass state. We show that the anomalous magnetic behavior of the high-field paramagnetic superconductor NdFeAs(O(1-x)F(x)) is mostly determined by the magnetic Nd(3+) ions, which rules out intrinsic long-range antiferromagnetism on the FeAs plane in the superconducting state.